Foundry process for bronze pouring


Smith uses a method of casting called the Lost-Wax Process, also know as cire-perdue. This method creates a metal duplicate from an original sculpture by the pouring of molten metal into a mold created by a wax model that was formed from the original sculpture. This method is said to date back to the 3rd millennium BC and was widely used across Europe until the 18th century. The process is slow and tedious with many steps but is arguably the best method to obtain high-quality bronzes.


Once the original clay sculpture is finished by Smith it is sent to the foundry to be transformed. After the sculpture is received the foundry begins the lost-wax process.

Rubber Mold in Lost wax process at foundry


The mold-making begins by a liquid rubber mixture being applied to the original sculpture. This mixture is hand applied by brush to make sure it gets into even the tiniest crevices, picking up the fingerprints and texture marks left behind by the sculptor. The liquid rubber is allowed to dry in between layers until it forms a thick soft layer creating an inner mold.  A hard outer layer or the "mother mold" is created using plaster. The plaster is applied to the outside of the rubber mold by hand stopping to allow layers to dry until the plaster mold is complete. Once the rubber mold and plaster mold are finished they are an exact negative of the original sculpture. Depending on the size and other factors of the piece, the original clay sculpture might be cut into sections to be molded resulting in multiple molds for a single sculpture.

Octopus Wax Model for Scupture in Lost Wax Proccess at Foundry


The mold is then used to create the wax model. Since most sculptures are hollow the melted wax is applied in layers. The wax is poured into the mold and swished around to obtain and even layer inside the mold. The excess wax is poured out and the layer is allowed to cool before the next batch of melted wax is poured into the mold and the process is repeated until the desired thickness is achieved. When complete and cooled the wax model is removed from the mold. The mold can be stored for later use.

Wax Models for Bronze Sculpture at Foundry


Now that a wax model has been created it goes through a process called chasing. This is where all the bubbles, mold lines, and any imperfections are filled and smoothed with heat and wax to make the wax model as close to the original sculpture as possible.

When the chasing is complete the wax channels called "sprues" or "gates" made of tree-like structure of wax are attached inside the wax model then a "cup" is placed on top and attached to the structure of sprues. These channels will act as funnels for the liquid bronze, allow air to escape and eventually enable the wax to melt out of the shell.

Ceramic Shell of Sculptures at Foundry


Once the wax model is complete it is dipped in a liquid ceramic mixture then covered in fine sand. When this first coat is dried these steps are completed until the desired thickness is obtained. Now there is a ceramic mold with the wax model still inside.

Cermaic Shells in Kiln at Foundry for Sculptures


After the ceramic shell is finished it is placed into a furnace to cure. During this step the wax model melted out, and we are left with the ceramic shell which includes the sprues and cup.

This is where the name "lost-wax" originated. Since each sculpture has to have a wax model and each time a bronze is poured the wax is lost when melted away.

Liquid bronze being poured in cermaic shell mold for sculpture


The empty ceramic shell is now filled with molten bronze. The bronze around, 2100 degrees Fahrenheit, is poured into the cup and flows through the "sprues" into the negative space.

Raw Bronze of Sculpture at Foundry


After the bronze has cooled the ceramic shell is broken away revealing the raw bronze sculpture.

Raw Bronze Conch Sculpture at Foundry


Following the removal of the ceramic shell, we are left with rough bronze. At this stage, if the sculpture was cast in multiple pieces the separate pieces will be welded together.  Now it will be sandblasted, cleaned and chased to bring it back to a copy of the original clay sculpture. This is done with such care and precision you will not be able to tell that it was more than one piece.


Pelican Sculpture During Patina Process at Foundry


The last step before the sculpture is ready for its new home is the patina process. This is where the color is added. By heating the bronze and applying different combinations of chemicals, acids, and pigments many different color variations can be achieved. Once the patina is finished a layer of wax is applied to the sculpture for protection.